1. Field of the Invention
The invention relates generally to a loading tray for loading particulate material into an array of tubes. More particularly the invention relates to catalyst loading tray for loading particulate catalyst into reactor tubes of catalyst reactors. In other aspects, the invention relates to a loading tray element for assembly into a loading tray; and a method of loading particulate catalyst into a catalytic reactor using a catalyst loading tray. In particular the invention relates to a device and method for loading catalyst pellets into catalytic reactor vessels having a plurality of vertically aligned, parallel reaction tubes.
2. Description of the Related Art
Chemicals are often manufactured on an industrial scale by reaction in large industrial catalytic reactors. A type of industrial catalytic reactor often used is provided with a multitude of vertically arranged, parallel reaction tubes partially or fully filled with catalyst particles during operation. Chemical reactants are passed through the reaction tubes to contact the catalyst for reaction. Such reactors are often referred to as multi-tube reactors. These types of reactors are known and are described in patent publications GB3,223,490 and U.S. Pat. No. 6,409,977.
Typical catalytic reactors are cylindrical with a diameter in the region of 2 to 9 metres and a height in the region of 5 to 50 metres. Catalytic reactors are usually bespoke structures designed for particular chemical processes or site requirements and hence individual reactors can vary greatly in their dimensions. In principle, such a reactor can be of any size, and in particular can be bigger or smaller than the typical sizes given above, the limitations being associated with physical construction limits and reaction requirements. There has been a general trend in the last years, particularly in the petrochemical industry, to increase catalytic reactor sizes.
The reactor is normally provided with a cylindrical shell containing a large number of vertically aligned, parallel reaction tubes; anywhere from 500 to 40,000. The reaction tubes have upper and lower ends that are joined e.g. welded, to openings in upper and lower tube sheets. The tube sheets extend horizontally in the cylindrical shell and are normally located adjacent end flanges thereof. The upper and lower ends of the reactor shell are closed off by domes that can be opened to permit internal access for servicing and catalyst replacement in the reaction tubes. For example, the domes may be provided with manholes to allow worker access or may be removable. Oftentimes domes are non-removable, or at least not conveniently removable, because cooling pipes are run through the dome into the reactor core. These cooling pipes can make it complicated or impossible to remove the dome of the reactor.
The reaction tubes are open at their ends and can have inner diameters from in the region of about 2 to 15 cm. They are joined (e.g. by welding), to a pattern of openings provided in the tube sheets. The number of tubes and pattern of openings in the tube sheets is appropriate to the chemical reaction and scale of reaction that is carried out in the reactor, but normally the openings are equally spaced with a, preferably constant, pitch (i.e. the shortest distance between the outer periphery of one hole and the outer periphery of its neighbour hole) of from 0.3 to 5 cm or more.
Catalyst particles are loaded into the reaction tubes. Catalyst particles are provided in a variety of sizes and shapes, typically spherical or cylindrical, and have nominal diameters in the range of from about 1 mm to 25 mm, more normally in the range of 2 to 1.5 mm. The reaction tubes and catalyst pellets are matched in size to allow for the particles to enter the reaction tubes in a controlled manner that minimizes bridging risks. Typically the particles have a maximum dimension of from 0.1 to 0.8 times the reaction tube inner diameter, more normally from 0.15 to 0.6, and more normally 0.25 to 0.4.
Careful loading of the catalyst particles into the reaction tubes is essential to ensure that the catalyst reaction proceeds as desired. In particular, it is necessary to: achieve the correct loading density of particles within a reaction tube; to make sure that each of the reaction tubes has a similar pack density within a tolerance range; to avoid bridging, i.e. void formation when two or more particles wedge against one another in the tube forming a false base; to provide filling of the catalyst to the correct level in the reaction tube i.e. allowing sufficient tube outage when needed; to avoid as far as possible dust entry into the reaction tubes; and to avoid crushing and/or attrition of catalyst particles by harsh filling practices. When loading catalyst into the reactor tubes it is best to limit the loading orifice so that catalyst particles enter one by one, predominantly because this reduces the risk of bridging.
Bearing these requirements in mind, loading of catalyst into a large number of reaction tubes in a catalytic reactor is both time consuming and arduous. This leads to excessive down-time of expensive reactor plants, and also to possible errors in filling, leading to poor quality reactions and products.
A conventionally used loading method is template loading. In such a method a large custom template is provided. The template forms a grid of holes with spacing that matches the layout of the reactor tube ends in the tubesheet. The template is laid over the tubesheet of the reactor. Catalyst is poured onto the template and is loaded into the reactor tube ends by up to four persons sweeping the catalyst over the template.
It has been attempted in the prior art to accelerate the filling of catalyst into catalytic reactors by provision of filling aids.
WO98/14392 and U.S. Pat. No. 4,402,643 discuss reaction tube charging systems. The systems take the form of wheeled loading carts with multiple catalyst charging tubes for simultaneous insertion into a multitude of reaction tubes. The carts can be wheeled over the tube sheets.
U.S. Pat. No. 3,913,806 discusses a catalyst loader for simultaneous loading of catalyst particles into multiple tubes. The catalyst loader takes the form of a movable support frame including a number of tubular members which hold a predetermined quantity of catalyst material for deposit into the reaction tubes. The frame is used to fill a number of reaction tubes and is then moved to another set of empty reaction tubes to fill those tubes.
U.S. Pat. Nos. 3,223,490 and 2,985,341 discuss catalytic reactor loaders in the form of templates that sit atop the tubesheet. In U.S. Pat. No. 2,958,341, the template is aligned with the openings in the tubesheet and catalyst particles are poured onto the template from where they are vibrated into the openings and into the reaction tubes. WO2010/068094 discusses a loading device having a plate with a pattern or loading holes provided with a sieving means between the loading holes. The device covers an array of reaction tube openings while providing for dust removal.
U.S. Pat. No. 5,906,229 discusses a catalyst loader that fills multiple tubes at one time by allowing catalyst particles to rain down over the reaction tube openings.
EP0963785 discusses reactor tube inserts with polygonal heads that make up a loading surface with regular gapping between the insert heads. The gapping forms a recess for collecting dust when catalyst particles are swept over the inserts.
WO2010/068094 discusses a recent development in catalyst loading takes the form a parallelogram template with an array of in the region of 96 holes surrounded by an upstanding wall. The template is placed over a region of tubesheet fitted with filler sleeves. The loader template is then reciprocally shifted parallel to the tubesheet while catalyst particles are poured on. The reciprocal shifting provides for a sweeping of the particles into the reaction tubes. Such a device is known from Mourik International BV, Netherlands as The Shuffle Loader™. An advantage of this device is that it offers benefits of template loading while usable in almost any catalytic reactor having appropriate tube spacing (pitch) on the tubesheet.
Another problem that exists with conventional loading processes is found in the release and generation of catalyst dust and fines. Although catalyst material is typically sieved to remove dust at the point of manufacture or dispatch, not all dust can be removed and new dust and fines is unavoidably generated due to particle attrition during transport and loading.
Dust and fines are a problem because they can pollute the working environment for personnel; they can adversely affect the catalytic reaction in the vessel by increasing density of packing and by blocking reactant flow; and they can pollute reaction product.
Attempts have been made in the prior art to reduce the problem of dust and fines.
In WO2006/104832, US2006/0233631 and U.S. Pat. No. 4,077,530 for example, insertion of velocity reducing devices to the reaction tubes has been proposed so as to slow particles as they fall in the tubes.
U.S. Pat. No. 4,737,269 discusses a catalyst loading hopper provided with a dust outlet at the top of the hopper, which may be connected to a conduit so as to draw dust away from the upper end of the hopper and a screen at the bottom of the hopper to separate the catalyst from any fine or undersized catalyst particles. This apparatus can capture some of the dust generated due to attrition during transportation but improvement is desirable. In addition the apparatus does not address the matter of dust generated during loading of catalyst particles into the reaction tubes, by e.g. sweeping or vibration of the particles.
U.S. Pat. No. 3,409,411 discusses a method of separating fines from particulate catalyst during loading, by application of a vacuum. The catalytic reactor addressed is a flat-bed reactor that is loaded with a single hose, not with a catalyst loading template.
There remains a need for improved filling practices and filling apparatuses.